I did change both gears. I didn't change the clutch thing that makes it shift thow. But i did do several adjustments on it to see if it did shift but it never got to a decent speed to shift. when i take off it does hesitate. Some one else told me to make sure i don't have any air leaks in the fuel lines or exhaust. A while ago i tried it again. I notice when the fuel is going thru the fuel line, there are several air bubbles going thru also. Could this be the cause of the problem?